Specifications

please add

Internals

The trigger signal passes through source switching, coupling switching, and then a JFET source-follower buffer.
Next, the signal is buffered by a PNP emitter-follower biased at around 5mA collector current.
That provides a known (low) source impedance for driving the switch-selectable LF reject and HF reject filters.
The output of the filters drives a discrete NPN differential amplifier, which drives U165, a 155-0109-01 Tek-made trigger IC.